Multiple transmit antenna interleaver design

ABSTRACT

An arrangement of interleavers allocates bits from an input symbol across sub-symbols transmitted via sub-carriers of multiple orthogonal frequency division multiplex (OFDM) carriers. The input bits are allocated in a fashion to provide separation across subcarriers, and rotation of sub-symbols across the OFDM carriers provides additional robustness in the present of signal path impairments.

CROSS REFERENCE TO RELATED APPLICATIONS

The present U.S. Utility patent application claims priority pursuant to35 U.S.C. §120, as a continuation, to the following U.S. Utility patentapplication which is hereby incorporated herein by reference in itsentirety and made part of the present U.S. Utility patent applicationfor all purposes:

1. U.S. Utility application Ser. No. 13/372,703 entitled “MultipleTransmit Antenna Interleaver Design,” (Attorney Docket No. BP3690C1),filed Feb. 14, 2012, pending, which application claims priority pursuantto U.S. 35 U.S.C. §120, as a continuation of U.S. Utility application.Ser. No. 11/137,259, filed May 25, 2005, now U.S. Pat. No. 8,139,659,which makes reference to, claims priority to, and claims benefit of U.S.Provisional Patent Application Ser. No. 60/574,108, entitled “MultipleTransmit Antenna Interleaver Design” (Attorney Docket No. 15807US01BP3690), filed May 25, 2004, U.S. Provisional Patent Application Ser.No. 60/582,223, entitled “Multiple Transmit Antenna Interleaver Design”(Attorney Docket No. 15875US01 BP3690.1), filed Jun. 22, 2004, and U.S.Provisional Patent Application Ser. No. 60/587,315, entitled “MultipleTransmit Antenna Interleaver Design” (Attorney Docket No. 15879US01BP3690.2), filed Jul. 13, 2004, the complete subject matter of each ofwhich is hereby incorporated herein by reference, in their entirety.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[Not Applicable]

MICROFICHE/COPYRIGHT REFERENCE

[Not Applicable]

BACKGROUND OF THE INVENTION

Simple receivers assume independent noise samples at each time instantand independent channel fades. In reality, bursts of errors occur andthe channels at different time instants are correlated. Convolutionalcoded data, for example, can only handle small bursts of errors. Thegoal of an interleaver is to randomize the transmitted data stream so asto make decoding at the receiver simple. A well-designed interleaverspreads the error burst over time so that the convolutional code canhandle it. Wireless LAN systems currently exploit the frequencydimension and do not take advantage of the time dimension. This is dueto the large coherence time of the channel and the inherent delay thatwould be associated with an interleaver that took advantage of bothfrequency and time dimensions.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of skill in the art, throughcomparison of such systems with some aspects of the present invention asset forth in the remainder of the present application with reference tothe drawings.

BRIEF SUMMARY OF THE INVENTION

A system and/or method for interleaving data for transmission overmultiple antennas, substantially as shown in and/or described inconnection with at least one of the figures, as set forth morecompletely in the claims.

These and other advantages, aspects, and novel features of the presentinvention, as well as details of illustrated embodiments, thereof, willbe more fully understood from the following description and drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows a high-level block diagram of an exemplary communicationsystem in which a representative embodiment of the present invention maybe practiced.

FIG. 2 shows a block diagram of an exemplary communication system thatmay correspond, for example, to a portion of the OFDM transmitter shownin FIG. 1 for processing a sequence of transmit data bits fortransmission as two OFDM signals #0 and #1, in accordance with arepresentative embodiment of the present invention.

FIG. 3 shows a block diagram of an exemplary interleaver block that maycorrespond, for example, to the interleaver block of FIG. 2 forprocessing a sequence of data bits for transmission using two transmitantennas, in accordance with a representative embodiment of the presentinvention.

FIG. 3A illustrates an exemplary interleaver block processing the bitsof an input symbol to produce two transmit streams #0 and #1 that maycorrespond, for example, to the transmit streams #0 and #1,respectively, of FIG. 3, in which a representative embodiment of thepresent invention may be practiced.

FIG. 4 shows a block diagram of an exemplary interleaver block forprocessing a block of input bits to a sequence of output bits fortransmission over multiple transmit streams, in accordance with arepresentative embodiment of the present invention.

FIG. 5 illustrates the permutation of a block of input bits by anexemplary interleaver that produces a sequence of output bits, accordingto interleaving algorithms specified in the IEEE 802.11a and IEEE802.11g standards.

FIG. 6 illustrates the permutation of a block of input bits by anotherexemplary interleaver that produces a sequence of output bits, accordingto interleaving algorithms specified in the IEEE 802.11a and IEEE802.11g standards.

FIG. 7 illustrates the permutation of a block of input bits to asequence of output bits by an exemplary interleaver block that maycorrespond, for example, to the interleaver block of FIG. 3, inaccordance with a representative embodiment of the present invention.

FIG. 8 illustrates the processing by an exemplary interleaver block of ablock of input bits to produce a sequence of output bits comprising twosubsequences of output bits for transmission via two OFDM transmitsignals such as, for example, the OFDM signals #0 and #1 of FIG. 2, inaccordance with another representative embodiment of the presentinvention.

FIG. 9 illustrates the processing by an exemplary interleaver block of ablock of input bits to produce a sequence of output bits comprising twosubsequences of output bits for transmission via two OFDM transmitsignals such as, for example, the OFDM signals #0 and #1 of FIG. 2, inaccordance with another representative embodiment of the presentinvention.

FIG. 10 illustrates the processing by an exemplary interleaver block ofa block of input bits to produce a sequence of output bits comprisingtwo subsequences of output bits for transmission via, for example, twoOFDM transmit signals such as the OFDM signals #0 and #1 of FIG. 2, inaccordance with another representative embodiment of the presentinvention.

FIG. 11 illustrates an exemplary sequence of output bits comprisingthree subsequences of output bits for transmission via, for example,three OFDM transmit signals, the sequence of output bits produced by aninterleaver block such as, for example, the interleaver block of FIG. 8,in accordance with another representative embodiment of the presentinvention.

FIG. 12 illustrates an exemplary sequence of output bits comprisingthree subsequences of output bits for transmission via, for example,three OFDM transmit signals, where the sequence of output bits areproduced by an interleaver block such as, for example, the interleaverblock of FIG. 10, in accordance with another representative embodimentof the present invention.

FIG. 13 illustrates another exemplary sequence of output bits comprisingthree subsequences of output bits for transmission via, for example,three OFDM transmit signals, where the sequence of output bits areproduced by an interleaver block such as, for example, the interleaverblock of FIG. 8, in accordance with a representative embodiment of thepresent invention.

FIG. 14 is a graph comparing the estimated performance of communicationsystems employing existing (i.e., legacy, IEEE 802.11a/g) interleavingtechniques and one transmit and one receive antenna, no bit interleavingusing one transmit and one receive antenna, a system employing fourtransmit and four receive antennas without interleaving, and a systememploying four transmit and four receive antennas with interleaving inaccordance with a representative embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Aspects of the present invention relate to the transmission of data overa medium subject to fading and noise. More specifically, certain aspectsof the present invention pertain to a method of interleaving bits of asequence of data bits for transmission via radio frequency signals usingmultiple transmit antennas. Although embodiments of the presentinvention are described below with respect to applications intransmitting a sequence of data bits via a particular exemplary radiofrequency wireless communication system, an embodiment of the presentinvention is not limited in this regard, and may have utility withregard to other communication mechanisms such as, for example, opticalcommunication, without departing from the spirit or scope of the presentinvention. In addition, the following discussion makes reference toexemplary embodiments employing a particular number (e.g., 48) ofsubcarriers (also known as “tones”) in an orthogonal frequency divisionmultiplex signal. The number of subcarriers used herein in illustratingaspects of the present invention is not intended to represent a specificlimitation of the present invention. The examples of the text andfigures are provided for illustrative purposes only, as a greater orlesser number of subcarriers may be employed without departing from thespirit and scope of the present invention.

FIG. 1 shows a high-level block diagram of an exemplary communicationsystem 100 in which a representative embodiment of the present inventionmay be practiced. As shown in FIG. 1, the communication system 100comprises a radio frequency (RF) transmitter 120 employing orthogonalfrequency division multiplexing (OFDM) to transmit a sequence of databits 105. The OFDM transmitter 120 shown in FIG. 1 employs multipletransmit antennas 132 a, 132 b to convey RF signals 135 a, 135 b toreceiving antennas 133 a, 133 b connected to an OFDM receiver 140. TheOFDM receiver 140 converts the received RF signal to a sequence ofreceived data bits 145. Although the OFDM transmitter 120 is shown ashaving two transmit antennas 132 a, 132 b, this is for illustrativepurposes only and does not represent a limitation of the presentinvention. A greater number of transmit antennas may be employed withoutdeparting from the spirit or scope of the present invention.

FIG. 2 shows a block diagram of an exemplary communication system 200that may correspond, for example, to a portion of the OFDM transmitter120 shown in FIG. 1 for processing a sequence of transmit data bits 205for transmission as two OFDM signals #0 230 a and #1 230 b, inaccordance with a representative embodiment of the present invention. Asillustrated in FIG. 2, the communications system 200 comprises acombination of functional blocks including a convolutional encoder block210, an interleaver block 215, bit-to-symbol mapper blocks 220 a, 220 b,pilot and guard tone insertion blocks 222 a, 222 b, inverse fast Fouriertransform (IFFT) blocks 224 a, 224 b, prefix insertion blocks 226 a, 226b, and I/Q modulator blocks 228 a, 228 b. It is a function of thecommunication system 200 of FIG. 2 to process the sequence of transmitdata bits 205 into two orthogonal frequency division multiplex (OFDM)signals 230 a, 230 b for transmission via radio frequency carriers suchas, for example, the RF paths 135 a, 135 b of FIG. 1. The convolutionalencoder 210 receives the sequence of transmit data bits 205 and producesan encoded output 212 that is then passed to the interleaver block 215.The interleaver block 215 distributes interleaved and grouped sequencesof sub-symbols of transmit streams 218 a, 218 b to bit-to-symbol mappers220 a, 220 b, respectively. For each of the transmits streams 218 a, 218b, a subsequence exists that corresponds to a set of bits to betransmitted. The bit-to-symbol mappers 220 a, 220 b may pass, forexample, mappings to inverse fast Fourier transform blocks 224 a, 224 b,respectively. Signals from pilot and guard tone insertion blocks 222 a,222 b are also combined with the signals being transformed. The outputsof the inverse fast Fourier transform blocks 224 a, 224 b are combinedwith signals from prefix insertion blocks 226 a, 226 b and passed to I/Qmodulator blocks 228 a, 228 b, respectively, to produce OFDM signals #0230 a and #1 230 b.

Although the communication system 200 illustrated in FIG. 2 comprises aparticular arrangement of functional blocks for communicating thesequence of transmit data bits 205 using two transmit antennas, this isfor illustrative purposes only and does not represent a specificlimitation of the present invention. A different arrangement or numberof components supporting transmission using a greater number of transmitantennas may be employed without departing from the spirit or scope ofthe present invention.

FIG. 3 shows a block diagram of an exemplary interleaver block 315 thatmay correspond, for example, to the interleaver block 215 of FIG. 2 forprocessing a sequence of data bits for transmission using two transmitantennas, in accordance with a representative embodiment of the presentinvention. The interleaver block 315 of FIG. 3 comprises a firstinterleaver 313, a second interleaver 314, a block mapper 316, and athird interleaver 317. Although the interleaver block 315 is shown ashaving a particular number and arrangement of interleavers and blockmappers, a greater or lesser number of interleavers and block mappersmay be employed without departing from the spirit and scope of thepresent invention. In a representative embodiment of the presentinvention, the interleaver 315 may be defined by a process having foursteps corresponding to the first interleaver 313, the second interleaver314, the block mapper 316, and the third interleaver 317 shown in FIG.3. A sequence of transmit data bits 312 that may correspond, forexample, to the output of an encoder such as the output 212 of theencoder 210 of FIG. 2, may be interleaved by a block interleaver using ablock size corresponding to the number of bits in a single orthogonalfrequency division multiplex (OFDM) symbol (N*N_(CBPS)) to producetransmit streams #0 318 a and #1 318 b. The transmit streams #0 318 aand #1 318 b may correspond, for example, to the transmit stream 218 aand 218 b of the interleaver 215 of FIG. 2. For each of the streams 318a, 318 b a subsequence exists that corresponds to a set of bits to betransmitted. In a representative embodiment of the present invention,the permutations of the interleavers 313, 314, 316, 317 may comprisepermutations defined in the Institute of Electrical and ElectronicsEngineers, Inc. (IEEE) 802.11a and 802.11g standards. Details of theIEEE 802.11a standard may be found in IEEE Std 802.11a-1999, alsore-designated as ISO/IEC 8802-11:1999/Amd 1:2000(E), the completesubject matter of which is hereby incorporated herein by reference, inits entirety. Details of the IEEE 802.11g standard may be found in IEEEStd 802.11g-2003 (Amendment to IEEE Std 802.11, 1999 Edition (Reaffirmed2003) as amended by IEEE standards 802.11a-1999, 802.11b-1999,802.11b-1999/Cor 1-2001, and 802.11d-2001), the complete subject matterof which is hereby incorporated herein by reference, in its entirety.

In the following discussion of various aspects of the present invention,the parameters shown below may be defined:

N_(CBPS) Number of bits per (OFDM) symbol

N: Number of data streams to be transmitted

B: Number of bits per subcarrier

K: Number of subcarriers per (OFDM) symbol

r: Interleaving depth or “base”

In a representative embodiment of the present invention, interleaver 313of FIG. 3 may perform a first permutation upon the bits of the inputsymbol according to the following formula:

$\begin{matrix}{{i = {{\frac{BKN}{r}( {k\; {mod}\; r} )} + \lfloor \frac{k}{r} \rfloor}}{{k = 0},1,{{\ldots \mspace{14mu} {BKN}} - 1}}} & (1)\end{matrix}$

where k denotes the index of the input bits as they enter theinterleaver, i denotes the index of the k^(h) input bit in the output ofinterleaver 313, and └•┘ denotes the floor operation (i.e., having avalue equal to the largest integer not exceeding the argument). For aninterleaver such as, for example, interleaver 313 operating according tothe IEEE 802.11a or IEEE 802.11g standards in which BPSK is used withK=48 subcarriers (also known as “tones”), the above formula becomes:

$i = {{3( {k\; {mod}\; 16} )} + \lfloor \frac{k}{16} \rfloor}$k = 0, 1, …  47

while the formula for the use of QPSK becomes:

$i = {{6( {k\; {mod}\; 16} )} + \lfloor \frac{k}{16} \rfloor}$k = 0, 1, …  95

Use of the above permutations result in a three tone separation betweenadjacent input bits in the output stream.

In a representative embodiment of the present invention, interleaver 314of FIG. 3 may perform a second permutation upon the output bits ofinterleaver 313 according to the following formula:

$\begin{matrix}{{j = {{s\lfloor \frac{i}{s} \rfloor} + {{mod}( {{i + {B\; K\; N} - \lfloor \frac{ri}{B\; K\; N} \rfloor},s} )}}},{i = 0},1,{{\ldots \mspace{14mu} B\; K\; N} - 1}} & (2)\end{matrix}$

where s=max(B/2,1), i denotes the index of the input bits as they enterinterleaver 314, j denotes the index of the i^(th) input bit in theoutput of interleaver 314, and r denotes the depth or “base”, asdescribed above. The number of data subcarriers (also known as “tones”),K, may be related to the number of bits per subcarrier B, and the numberof bits per (OFDM) symbol N_(CBPS) by the formula:

$K = {\frac{N_{CBPS}}{B}.}$

In a representative embodiment of the present invention, a block mapper,shown as the block mapper 316 in FIG. 3, may ensure that bits are spreadacross the transmit streams before being spread across subcarriers, andmay group one or more sub-symbols into blocks. Bits from the output ofinterleaver 314 may be grouped into sub-symbols of size B, and thesub-symbols may be grouped into blocks of size

$\frac{K}{rot},$

where rot is as defined below.

In a representative embodiment of the present invention, the parameterrot may determine the width of a data block within a transmit streamsuch as, for example, the transmit stream #0 318 a of FIG. 3. In arepresentative embodiment of the present invention, the value of theparameter rot may be selected as any divisor of K (i.e., the number ofsubcarriers or “tones”) that is greater than or equal to the number oftransmit streams, N. The width of a data block is then given by

$\frac{K}{rot},$

and the number of data blocks transmitted via each stream is equal torot. In a representative embodiment of the present invention, a block pmay comprise sub-symbols

$\{ {\frac{Kp}{rot},{\frac{Kp}{rot} + 1},\ldots \mspace{14mu},{{( {p + 1} )\frac{K}{rot}} - 1}} \}$for  0 ≤ p ≤ N * rot − 1.

In a representative embodiment of the present invention, the interleaver317 may function to swap or rotate sub-symbols between a firstsubsequence for a first transmit stream such as, for example, thetransmit stream 318 a, and a second subsequence for a second transmitstream such as, for example, the transmit stream 318 b.

FIG. 3A shows a block diagram of an exemplary interleaver block 300 forprocessing a block of input bits 310 to a sequence of output bits 318for transmission over multiple transmit streams, in accordance with arepresentative embodiment of the present invention. The interleaver 300shown in FIG. 3A comprises a series of interleavers represented in FIG.3A by interleavers 312, 314, 316 for converting the block of input bits310 to the output bit sequence 318. Although three interleavers areshown in the illustration of FIG. 3A, a different number of interleaversmay be employed without departing from the spirit or scope of thepresent invention. The sequence of interleavers 312, 314, 316 may, forexample, perform the functionality represented by the interleaver block315 of FIG. 3. The sequence of output bits 318 shown in FIG. 3Acomprises a number of subsequences such as subsequences 320 a, 320 b,each subsequence designated for transmission using a separate transmitstream such as, for example, the transmit streams #0 318 a, #1 318 b ofFIG. 3. For example, in a representative embodiment of the presentinvention in which two transmit streams are used, the output bitsequence 318 may comprise two subsequences 320 a, 320 b, where each ofsubsequences 320 a, 320 b are designated for transmission via one of thetwo transmit streams.

In a representative embodiment of the present invention, bits within asubsequence such as, for example, the subsequence 320 a may be arrangedinto multiple groups or sub-symbols 322, 324, where each sub-symbol isallocated for transmission via one of the subcarriers or “tones” of anOFDM signal such as, for example, the OFDM signals 230 a, 230 b shown inFIG. 2. For example, in a representative embodiment of the presentinvention in which binary phase shift keyed (BPSK) modulation isemployed for each subcarrier, each of the groups 322, 324 may compriseone bit of the sequence of output bits 318. In a representativeembodiment in which quadrature phase shift keyed (QPSK) modulation isemployed for each subcarrier, each of the groups 322, 324 may comprisetwo bits of the sequence of output bits 318. In a system in which Ksubcarriers or tones are employed, the size of the subsequence 320 a maybe K bits using, for example, BPSK, and 2*K bits when QPSK is used. Thetotal number of bits in each of the block of input bits 310, and thesequence of output bits 318 may be calculated as B*K*N, where B is thenumber of bits per sub-symbol, K is the number of subcarriers (alsoknown as “tones”) in each OFDM signal, and N is the number of transmitstreams.

FIG. 4 illustrates an exemplary interleaver block 415 processing thebits of an input symbol 410 to produce two transmit streams #0 418 a and#1 418 b that may correspond, for example, to the transmit streams #0318 a and #1 318 b, respectively, of FIG. 3, in which a representativeembodiment of the present invention may be practiced. The illustrationof FIG. 4 represents an arrangement using 48 (i.e., K=48) subcarriers(also known as “tones”), employing quadrature phase-shift keying (QPSK)(i.e., B=2), and two transmit streams, #0 318 a and #1 318 b (i.e.,N=2). Because the number of transmit streams, N is equal to 2, and thenumber of subcarriers per OFDM symbol, K, is equal to 48, there are atotal of 96 (i.e., K*N) sub-symbols per input symbol. The firstsubcarrier of transmit stream #0 418 a comprises sub-symbol #0 452 a,which is composed of input symbol 410, bits 0 and 16. The nextsubcarrier comprises sub-symbol #1 454 a, which is composed of inputsymbol 410, bits 64 and 80. The last subcarrier of stream #0 418 acomprises sub-symbol #47 456 a, which is composed of input symbol 410,bits 143 and 159. The first sub-symbol #48 452 b of transmit stream #1418 b is composed of input symbol 410, bits 32 and 48. The lastsubcarrier of stream #1 418 b comprises sub-symbol #95 456 b, which iscomposed of input symbol 410, bits 175 and 191. The collection ofsub-symbols #0 452 a through #95 456 b may then be grouped into datablocks as described below.

In a representative embodiment of the present invention, a thirdpermutation operation improves the performance of the communicationsystem 100 of FIG. 1 by rotating the N*rot data blocks across the Ntransmit streams. The following vector may be used as an indicator ofthe order of blocks to transmit.

m={(rot*q*(N−1)+p)mod(N*rot)p=N*(0:rot−1)+q0≦q≦N−1},  (3)

where the notation (0: rot−1) represents the sequence of indices 0, 1,2, . . . (rot−1).

For example, for the QPSK example illustrated above, a value of rot=48may correspond to transmitting data blocks 0, 49, 2, 51, . . . , 95 ontransmit stream #0 418 a, and data blocks 48, 1, 50, 3, . . . , 47 ontransmit stream #1 418 b.

A representative embodiment of the present invention may use r=K/3 androt=K, when 48 subcarriers are used (K=48) in transmitting via twotransmit streams. A representative embodiment of the present inventionusing four transmit streams may employ values of r=K/2, and rot=K/2.When using three transmit streams, a representative embodiment of thepresent invention may use values of r=K/4 and rot=K. In a representativeembodiment of the present invention, the value of r may be selected tobe a large divisor of K, and the value of rot may be selected such thatit is not equal in value to K/r.

In accordance with a representative embodiment of the present invention,an additional arrangement employing three transmit streams may also beemployed, through the use of the following ordering:

$\begin{matrix}{m = \begin{Bmatrix}j & {{j = 0},2,4,{{\ldots \mspace{14mu} 3*( {{rot} - 1} )} + 1}} \\{( {{{rot}*( {N - 1} )} + j} ){{mod}( {N*{rot}} )}} & {{j = 1},5,9,{\ldots \mspace{14mu} 3*( {{rot} - 1} )}} \\{( {{{rot}*( {N - 2} )} + j} ){{mod}( {N*{rot}} )}} & {{j = 3},7,11,{{\ldots \mspace{14mu} 3*( {{rot} - 1} )} + 2}}\end{Bmatrix}} & (4)\end{matrix}$

FIG. 5 illustrates the permutation of a block of input bits 510 by anexemplary interleaver 512 that produces a sequence of output bits 514,according to interleaving algorithms specified in the IEEE 802.11a andIEEE 802.11g standards. The interleaver 512 may correspond, for example,to one of the interleavers 312, 314, 316 of FIG. 3A. As illustrated inFIG. 5, the interleaver 512 may operate according to the followingformula:

$i = {{3( {k\; {mod}\; 16} )} + \lfloor \frac{k}{16} \rfloor}$k = 0, 1, …  47

The interleaver 512 may function to map the k^(th) bit of the block ofinput bits 510 to the i^(th) bit of the sequence of output bits 514.Although the example interleaver 512 of FIG. 5 is illustrated asprocessing a block of input bits 510 that is 48 bits in length, in arepresentative embodiment of the present invention, such an interleavermay be employed to process larger blocks of input bits employing formula(1), shown above.

FIG. 6 illustrates the permutation of a block of input bits 610 byanother exemplary interleaver 612 that produces a sequence of outputbits 614, according to interleaving algorithms specified in the IEEE802.11a and IEEE 802.11g standards. The interleaver 612 may correspond,for example, to one of the interleavers 312, 314, 316 of FIG. 3A. Asillustrated in FIG. 6, the interleaver 612 may operate according to thefollowing formula:

$i = {{6( {k\; {mod}\; 16} )} + \lfloor \frac{k}{16} \rfloor}$k = 0, 1, …  , 95

As in the example of FIG. 5, the interleaver 612 functions to map thek^(th) bit of the block of input bits 610 to the i^(th) bit of thesequence of output bits 614. The example interleaver 612 of FIG. 6illustrates the processing of a block of input bits 610 that is 96 bitsin length, to produce a sequence of output bits 614. The sequence ofoutput bits 614 is arranged into multiple sub-symbols such assub-symbols 616, 618, 620, 622 according to the formula given above whenthe number of bits per sub-symbol, B, is equal to two, the number ofsubcarriers (also known as “tones”) K is equal to 48, and the number oftransmit streams N is equal to one. Although the interleaver shown inFIG. 6 is illustrated as processing a block of input bits 610 having 96bits, a representative embodiment of the present invention may beemployed to process blocks of input bits having a lesser or greaternumber of bits.

FIG. 7 illustrates the permutation of a block of input bits 710 to asequence of output bits by an exemplary interleaver block 715 that maycorrespond, for example, to the interleaver block 315 of FIG. 3, inaccordance with a representative embodiment of the present invention. Asshown in FIG. 7, the interleaver block 715 comprises an interleaver 712,an interleaver 714, and a bit-to-stream allocator 713. In arepresentative embodiment of the present invention, the interleaver 1712 may function to map the k^(th) bit of the block of input bits 710 tothe i^(th) bit of a bit sequence b_(i) according to formula (1), shownabove. In the example of FIG. 7, the parameter B is equal to two, K isequal to 48, N is equal to 2, and r is equal to 16. Other values of B,K, N, and r are possible within the spirit and scope of the presentinvention.

In a representative embodiment in accordance with the present invention,the interleaver 714 may function to map the i^(th) bit of the sequenceof bits b_(i) from interleaver 712 to the j^(th) bit of a bit sequenceb_(j), according to formula (2), shown above. In the example of FIG. 7,the parameter B is equal to two, K is equal to 48, N is equal to 2, r isequal to 16, and s is equal to one. Other values of B, K, N, r, and smay be employed without departing from the spirit and scope of thepresent invention.

In a representative embodiment in accordance with the present invention,the bit-to-stream allocator 713 may function in one of two modesaccording to the state of a control signal 711. In the illustration ofFIG. 7 in which the control signal 711 is in a “0” state, thebit-to-stream allocator 713 may function to allocate bits from the bitsequence b_(j) produced by interleaver 714 to first fill a subsequenceof bits such as, for example, the subsequence 718 a in its entirety,before allocating bits from the bit sequence b_(j) to anothersubsequence of bits such as, for example, the subsequence 718 b.Although the sequence of output bits 716 shown in FIG. 7 comprises twosubsequences 718 a, 718 b, a greater or lesser number of subsequencesmay be employed without departing from the spirit and scope of thepresent invention.

The sequence of output bits 716 shown in FIG. 7 comprises twosubsequences 718 a, 718 b that may correspond, for example, to twotransmit streams such as the transmit streams #0 318 a and #1 318 bshown in FIG. 3. The subsequence 718 a may correspond, for example, tothe subsequence 320 a of FIG. 3A, while the subsequence 718 b maycorrespond to the subsequence 220 b of FIG. 3A. Each of the subsequences718 a, 718 b comprise pairs of bits from the block of input bits 710,such as the bits b₀, b₁₆ of subsequence 718 a, and bits b₈, b₂₄ ofsubsequence 718 b, located in column 720 of FIG. 7. These pairs of bitscorrespond, respectively, to one sub-symbol for one of the K subcarriersto be transmitted in via a transmit stream such as, for example, theOFDM signal #0 230 a of FIG. 2. For example, bits b₀, b₁₆ may beallocated to the first subcarrier of a first OFDM transmit signal, andbits b₈, b₂₄ may be allocated to the first subcarrier of a second OFDMtransmit signal. In the illustration of FIG. 7, the interleaver block715 may function so as to allocate bits of a block of input bits firstto all sub-symbols of a first subsequence of output bits, beforeallocating bits of the block of input bits to sub-symbols of a secondsubsequence of output bits.

A representative embodiment of the present invention as shown in FIG. 7provides a separation of six subcarriers (i.e., tones) between bits inthe sequence of output bits 716 for bits that are adjacent in the blockof input bits 710. For example, bit b₀ is assigned to the sub-symbol forthe first subcarrier in subsequence 718 a, while bit b₁ is assigned tothe sub-symbol for the fourth subcarrier in subsequence 718 a. Byassigning bits that are adjacent in the block of input bits 710 todifferent subcarriers of an OFDM transmit signal, a reduction incorrelation between adjacent bits and greater immunity to transmissionimpairments is realized.

FIG. 8 illustrates the processing by an exemplary interleaver block 815of a block of input bits 810 to produce a sequence of output bits 818comprising two subsequences of output bits 820 a, 820 b for transmissionvia two OFDM transmit signals such as, for example, the OFDM signals #0230 a and #1 230 b of FIG. 2, in accordance with another representativeembodiment of the present invention. The interleaver block 815 of FIG. 8may correspond, for example, to the interleaver block 315 of FIG. 3. Asshown in FIG. 8, the interleaver block 815 comprises an interleaver 812,an interleaver 814, and a bit-to-stream allocator 813. As describedabove with respect to FIG. 7, each pair of bits in a column of thesubsequences 820 a, 820 b shown in FIG. 8 may represent a sub-symbol fortransmission on the associated subcarrier (i.e., “tone”) of an OFDMsignal such as, for example, the OFDM signals #0 230 a and #1 230 b ofFIG. 2.

In a representative embodiment of the present invention, interleaver 812may function to map the k^(th) bit of the block of input bits 810 to thei^(th) bit of a sequence of bits b_(i) according to formula (1), shownabove. In the example of FIG. 8, the parameter B is equal to two, K isequal to 48, N is equal to 2, and r is equal to 16. Other values of B,K, N, and r are possible within the spirit and scope of the presentinvention.

In a representative embodiment in accordance with the present invention,interleaver 814 may function to map the i^(th) bit of the sequence ofbits b_(i) produced by interleaver 812 to the j^(th) bit of a bitsequence b_(p) in accordance with formula (2), shown above. In theexample of FIG. 8, the parameter B is equal to two, K is equal to 48, Nis equal to 2, r is equal to 16, and s is equal to one. Other values ofB, K, N, r, and s are possible within the spirit and scope of thepresent invention.

In a representative embodiment in accordance with the present invention,the bit-to-stream allocator 813 may correspond to, for example, thebit-to-stream allocator 713 of FIG. 7, and may function in the second ofthe two modes described above with respect to the bit-to-streamallocator 713 of FIG. 7. In the illustration of FIG. 8, the controlsignal 811 is in a “1” state, and the bit-to-stream allocator 813 mayfunction to allocate bits from the bit sequence b_(j) produced byinterleaver 814 to first fill a selected subcarrier or “tone” insubsequences of bits such as, for example, the subsequences 820 a, 820 bfor all of the transmit streams, before allocating bits from the bitsequence b_(j) to the next subcarrier or “tone” of the subsequences ofall transmit streams. Although the sequence of output bits 818 shown inFIG. 8 comprises two subsequences 820 a, 820 b, a greater or lessernumber of subsequences may be employed without departing from the spiritand scope of the present invention.

A representative embodiment of the present invention as shown in FIG. 8provides a separation of three subcarriers (i.e., tones) between bits inthe sequence of output bits 818, for bits that are adjacent in the blockof input bits 810. For example, bit b₀ is assigned to the sub-symbol forthe first subcarrier in subsequence 820 a, while bit b₁ is assigned tothe sub-symbol for the fourth subcarrier in subsequence 820 a. Byassigning bits that are adjacent in the block of input bits 810 todifferent subcarriers of an OFDM transmit signal, a reduction incorrelation between adjacent bits and greater immunity to transmissionimpairments is realized.

FIG. 9 illustrates the processing by an exemplary interleaver block 915of a block of input bits 910 to produce a sequence of output bits 918comprising two subsequences of output bits 920 a, 920 b for transmissionvia two OFDM transmit signals such as, for example, the OFDM signals #0230 a and #1 230 b of FIG. 2, in accordance with another representativeembodiment of the present invention. The interleaver block 915 of FIG. 9may correspond, for example, to the interleaver block 315 of FIG. 3. Asshown in FIG. 9, the interleaver block 915 comprises an interleaver 912,an interleaver 914, a bit-to-stream allocator 913, and an interleaver916. The interleaver block 915 receives a block of input bits 910 andproduces a sequence of output bits 918 comprising a first subsequence920 a, and a second subsequence 920 b. The first and second subsequences920 a, 920 b may correspond, for example, to the subsequences of bits320 a, 320 b shown in FIG. 3A. As described above with respect to FIG.7, each pair of bits in a column of the subsequences 920 a, 920 b shownin FIG. 9 may represent a sub-symbol for transmission on the associatedsubcarrier (i.e., “tone”) of an OFDM signal such as, for example, theOFDM signals #0 230 a and #1 230 b of FIG. 2.

In a representative embodiment of the present invention, interleaver 912of the interleaver block 915 may function to map the k^(th) bit of theblock of input bits 910 to the i^(th) bit of a sequence of bits b_(i),according to formula (1), shown above. In the example of FIG. 9, theparameter B is equal to two, K is equal to 48, N is equal to 2, and r isequal to 16. Other values of B, K, N, and r are possible within thespirit and scope of the present invention.

In a representative embodiment in accordance with the present invention,interleaver 914 may function to map the i^(th) bit of the sequence ofbits b_(i) from interleaver 912 to the j^(th) bit of a bit sequenceb_(j), in accordance with formula (2), shown above. In the example ofFIG. 9, the parameter B is equal to two, K is equal to 48, N is equal to2, r is equal to 16, and s is equal to one. Other values of B, K, N, r,and s are possible within the spirit and scope of the present invention.

In a representative embodiment in accordance with the present invention,the bit-to-stream allocator 913 may function in one of two modesaccording to the state of a control signal 911. In the illustration ofFIG. 9 in which the control signal 911 is in a “0” state, thebit-to-stream allocator 913 may function to allocate bits from the bitsequence b_(j) produced by interleaver 914 to first fill a subsequenceof bits for a first transmit stream in its entirety, before allocatingbits from the bit sequence b_(j) to fill another subsequence of bits foranother transmit stream.

In a representative embodiment of the present invention, interleaver 916may correspond to, for example, the interleaver 317 of FIG. 3, and mayfunction to swap or rotate sub-symbols such as, for example, thesub-symbols 922, 924, 926, 928, 930 between a first subsequence for afirst transmit stream such as, for example, subsequence 920 a, and asecond subsequence for a second transmit stream such as, for example,subsequence 920 b. For example, in the illustration of FIG. 9interleaver 912 and interleaver 914 may operate to produce a sequence ofbits that corresponds to the sequence of output bits 716 shown in FIG.7. The function of interleaver 916 of FIG. 9 may swap or rotate asub-symbol such as, for example, the sub-symbol comprising bits b₃₂, b₄₈of the subsequence 718 a of FIG. 7, and the sub-symbol comprising bitsb₄₀, b₅₆ of the subsequence 718 b of FIG. 7. This may produce thearrangement of bits shown in the sub-symbols in column 922 of thesubsequences 920 a, 920 b of FIG. 9. In a similar fashion, interleaver916 may also swap sub-symbols 924, 926, 928, 930 between subsequences920 a and 920 b. Although the illustration of FIG. 9 shows rotation orswapping of only five sub-symbols between two subsequences of bits, agreater number of sub-symbols and/or subsequences may be employedwithout departing from the spirit or scope of the present invention.

A representative embodiment of the present invention as shown in FIG. 9provides a separation of six subcarriers (i.e., tones) between bits inthe sequence of output bits 918 for bits that are adjacent in the blockof input bits 910. For example, bit b₀ is assigned to the firstsubcarrier in the subsequence 920 a, while bit b₁ is assigned to thefourth subcarrier in the subsequence 920 a. By assigning bits that areadjacent in the block of input bits 910 to different subcarriers of anOFDM transmit signal, a reduction in correlation of bits and greaterimmunity to impairments is realized.

FIG. 10 illustrates the processing by an exemplary interleaver block1015 of a block of input bits 1010 to produce a sequence of output bits1020 comprising two subsequences of output bits 1022 a, 1022 b fortransmission via, for example, two OFDM transmit signals such as theOFDM signals #0 230 a and #1 230 b of FIG. 2, in accordance with anotherrepresentative embodiment of the present invention. The interleaverblock 1015 of FIG. 10 may correspond, for example, to the interleaverblock 315 of FIG. 3. As shown in FIG. 10, the interleaver block 1015comprises an interleaver 1012, a bit-to-stream allocator 1013, and aninterleaver 1018. The interleaver block 1015 receives a block of inputbits 1010 and produces a sequence of output bits 1020 comprising a firstsubsequence 1022 a, and a second subsequence 1022 b. The first andsecond subsequences 1022 a, 1022 b may correspond, for example, tosubsequences of bits 320 a, 320 b shown in FIG. 3A. As described abovewith respect to FIG. 7, each pair of bits in a column of thesubsequences 1022 a, 1022 b shown in FIG. 10 may represent a sub-symbolfor transmission on the associated subcarrier (i.e., tone) of an OFDMsignal such as, for example, the OFDM signals #0 230 a and #1 230 b ofFIG. 2.

In a representative embodiment of the present invention, interleaver1012 of the interleaver block 1015 may function to map the k^(th) bit ofthe block of input bits 1010 to the i^(th) bit of a sequence of bitsb_(i), according to formula (1), shown above. In the example of FIG. 10,the parameter B is equal to two, K is equal to 48, N is equal to 2, andr is equal to 16. Other values of B, K, N, and r are possible within thespirit and scope of the present invention.

In a representative embodiment of the present invention, the interleaver1014 may function to allocate bits of the sequence b_(i) produced byinterleaver 1012 first to sub-symbols of the same subcarrier of each ofthe OFDM transmit signals, before then allocating bits of the sequenceb_(i) to sub-symbols of the next subcarrier of each OFDM transmitsignal. The allocating process continues until all bits of the sequenceof bits b_(i) have been allocated to sub-symbols for all subcarriers ofall OFDM transmit signals.

In a representative embodiment in accordance with the present invention,interleaver 1014 may function to map the i^(th) bit of the sequence ofbits b_(i) from interleaver 1012 to the j^(th) bit of a bit sequenceb_(p) in accordance with formula (2), shown above. In the example ofFIG. 10, the parameter B is equal to two, K is equal to 48, N is equalto 2, r is equal to 16, and s is equal to one. Other values of B, K, N,r, and s are possible within the spirit and scope of the presentinvention.

In a representative embodiment in accordance with the present invention,the bit-to-stream allocator 1013 may correspond to, for example, thebit-to-stream allocator 913 of FIG. 9, and may function in the second ofthe two modes described above with respect to the bit-to-streamallocator 913. In the illustration of FIG. 10, the control signal 1011is in a “1” state, and the bit-to-stream allocator 1013 may function toallocate bits from the bit sequence b_(j) produced by interleaver 1014to produce a bit sequence b_(w) in which bits are allocated to aselected subcarrier or “tone” for all transmit streams, beforeallocating bits from the bit sequence b_(j) to the next subcarrier or“tone” of all transmit streams.

In a representative embodiment in accordance with the present invention,interleaver 3 1016 may function to map the w^(th) bit of the sequence ofbits b_(w) produced by the bit-to-stream allocator 1013, to the m^(th)bit of a bit sequence b_(m) that is shown in FIG. 10 as sequence ofoutput bits 1020. The sequence of output bits 1020 shown in FIG. 10comprises subsequences 1022 a, 1022 b for transmission via two OFDMsignals such as, for example, the OFDM signals #0 230 a and #1 230 b ofFIG. 2.

In a representative embodiment of the present invention, the interleaver1016 may function to swap or rotate sub-symbols such as, for example,the sub-symbols in columns 1024, 1026, 1028, 1030, 1032 of FIG. 10between a first subsequence for a first transmit stream such as, forexample, the subsequence 1022 a, and a second subsequence for a secondtransmit stream such as, for example, subsequence 1022 b. For example,in the illustration of FIG. 10 interleaver 1012, interleaver 1014, andthe bit-to-stream allocator 1013 may operate to produce a sequence ofbits that corresponds to the sequence of output bits 818 shown in FIG.8. The function of interleaver 1016 may be to swap a sub-symbolcomprising, for example, the bits b₆₄, b₈₀ of subsequence 820 a, and thesub-symbol comprising bits b₉₆, b₁₁₂ of subsequence 820 b, to producethe arrangement of bits shown in the sub-symbols of column 1024 ofsubsequences 1022 a, 1022 b. In a similar fashion, interleaver 1016 mayalso swap sub-symbols in columns 1026, 1028, 1030, and 1032 betweensubsequences 1022 a and 1022 b. Although the illustration of FIG. 10shows the swapping or rotation of only five pairs of sub-symbols, agreater number of corresponding sub-symbols and/or a greater number ofsubsequences may be employed without departing from the spirit or scopeof the present invention.

The use of a representative embodiment of the present invention as shownin FIG. 10 results a separation of three subcarriers (i.e., tones)between bits in the sequence of output bits 1020, for bits that areadjacent in the block of input bits 1010. In addition, the interleaverblock 1015 of FIG. 10 provides additional de-correlation by assigningadjacent bits in the block of input bits 1010 to sub-symbols in adifferent subsequence of output bits. For example, in the illustrationof FIG. 10, bit b₀ is assigned to the sub-symbol for the firstsubcarrier in the subsequence 1022 a, while bit b₁ is assigned to thesub-symbol for the fourth subcarrier in subsequence 1022 b. By assigningadjacent bits in the block of input bits 1010 to sub-symbols indifferent output subsequences 1022 a, 1022 b and, therefore fortransmission on different OFDM transmit signals, an additional reductionin correlation between bits and greater immunity to transmissionimpairments is realized over subcarrier separation on a single OFDMtransmit signal.

FIG. 11 illustrates an exemplary sequence of output bits 1110 comprisingthree subsequences of output bits 1120 a, 1120 b, 1120 c fortransmission via, for example, three OFDM transmit signals, the sequenceof output bits 1110 produced by an interleaver block such as, forexample, the interleaver block 815 of FIG. 8, in accordance with anotherrepresentative embodiment of the present invention. The illustration ofFIG. 11 shows a portion of a block of 288 input bits (288=B*K*N, whereB=2, K=48, N=3) following processing by an interleaver block such as,for example, the interleaver block 815 of FIG. 8. In the illustration ofFIG. 8, the interleaver block 815 produces a sequence of output bits 818comprising two subsequences 820 a, 820 b for transmission via two OFDMsignals such as, for example, the OFDM signals #0 230 a and #1 230 b ofFIG. 2. In a similar fashion, a representative embodiment of the presentinvention may be employed to produce a sequence of output bits 1110comprising three subsequences 1120 a, 1120 b, 1120 c, as illustrated inFIG. 11, for transmission via three OFDM transmit signals. In therepresentative embodiment illustrated in FIG. 11, the bits from a blockof input bits (not shown) are allocated to sub-symbols in one of threesubsequences 1120 a, 1120 b, 1120 c that may correspond, for example, toone of three transmit streams similar to the transmit streams 318 a, 318b shown in FIG. 3.

An interleaver block in accordance with the present invention mayallocate bits from a block of input bits to sub-symbols of a sequence ofoutput bits by first allocating bits to a sub-symbol of a designatedsubcarrier in all subsequences, before allocating bits to sub-symbolsfor transmission via the next subcarrier, and so on. For example, thebits allocated to sub-symbols 616, 618, 620 in the sequence of outputbits 614 from the interleaver 612 of FIG. 6 may be allocated to thethree subsequences 1120 a, 1120 b, 1120 c in a round-robin fashion asshown in column 1152 of FIG. 11, for transmission using the firstsubcarrier of each of three OFDM signals. The next three sub-symbols ofthe sequence of output bits 614 may then be allocated to the nextsubcarrier (i.e., column 1154 of FIG. 11) of three OFDM transmitsignals, similar to the two OFDM signals 230 a, 230 b of FIG. 2, forexample. Succeeding sub-symbols may be allocated in a similar fashion tothe columns 1156 as shown by columns 1156, 1158, 1160, 1162, 1164, 1166,1168, 1170, 1172, and 1174. In a representative embodiment of thepresent invention, an interleaver block similar to, for example, theinterleaver block 815 of FIG. 8 may be employed to process a block ofinput bits such as, for example, the block of input bits 810, fortransmission via three OFDM signals. Only 12 sub-symbols for 12subcarriers of each of three OFDM signals are shown in FIG. 11, althoughin a communication system such as the communication system 100 of FIG. 1employing 48 subcarriers, an additional 36 subcarriers may be used. Thesub-symbols for the additional subcarriers have been omitted from FIG.11 for reasons of clarity.

FIG. 12 illustrates an exemplary sequence of output bits 1210 comprisingthree subsequences of output bits 1220 a, 1220 b, 1220 c fortransmission via, for example, three OFDM transmit signals, where thesequence of output bits 1210 are produced by an interleaver block suchas, for example, the interleaver block 1015 of FIG. 10, in accordancewith another representative embodiment of the present invention. Theillustration of FIG. 12 shows only a portion of a block of 288 inputbits (288=B*K*N, where B=2, K=48, N=3) following processing by aninterleaver block such as, for example, the interleaver block 1015 ofFIG. 10. Although FIG. 10 illustrates an interleaver block 1015 thatproduces a sequence of output bits 1020 comprising two subsequences 1022a, 1022 b for transmission via two OFDM signals, the present inventionis not limited to the particular embodiment of FIG. 10, and may beapplied to produce a greater number of subsequences of output bits. Thesequence of output bits 1210 is similar to the sequence of output bits1110 of FIG. 11, with the additional operation of swapping or rotatingselected columns of sub-symbols between the subsequences 1220 a, 1220 b,1220 c. In the representative embodiment illustrated in FIG. 12, thebits from a block of input bits (not shown) are allocated to sub-symbolsin one of three subsequences 1220 a, 1220 b, 1220 c that may correspond,for example, to one of three transmit streams similar to the transmitstreams 318 a, 318 b shown in FIG. 3.

In the illustration of FIG. 12, it can be seen that sub-symbols incolumns 1254, 1256, 1260, 1262, 1266, 1268, 1272, and 1274 have beenrotated between the subsequences 1220 a, 1220 b, 1220 c when compared tothe arrangements shown in columns 1154, 1156, 1160, 1162, 1166, 1168,1172, and 1174, respectively, of FIG. 11. For example, in FIG. 11 thebits b₉₆, b₁₁₂ from the block of input bits have been allocated to asub-symbol for the second subcarrier (column 1154) of the subsequence1120 a, whereas in the illustration of FIG. 12, the same bits b₉₆, b₁₁₂from the block of input bits are allocated to a sub-symbol for thesecond subcarrier (column 1254) of the subsequence 1220 b. In a similarfashion, in FIG. 11 the bits b₁₂₈, b₁₄₄ that are allocated to thesub-symbol for the second carrier (column 1154) of subsequence 1120 bare allocated in the example of FIG. 12 to the second subcarrier (column1254) of subsequence 1220 c. To complete the example, the bits b₁₆₀,b₁₇₆ that are allocated to the second subcarrier (column 1154) ofsubsequence 1120 c in FIG. 11 are instead allocated in the illustrationof FIG. 12 to the second carrier (column 1254) of subsequence 1220 a.Similar rotations of sub-symbols between the subsequences 1220 a, 1220b, 1220 c are performed between sub-symbols in columns 1160, 1166, and1172 of FIG. 11 and columns 1260, 1266, and 1272 of FIG. 12. As shown inFIG. 12, an interleaver block in accordance with a representativeembodiment of the present invention may perform a similar rotation ofsub-symbols, where the sub-symbols in columns 1156, 1162, 1168, and 1174of FIG. 11 are rotated from subsequence 1120 a to subsequence 1220 c,from subsequence 1120 b to subsequence 1220 a, and from subsequence 1120c to subsequence 1220 b to form columns 1256, 1262, 1268, and 1274 ofFIG. 12, respectively. Only 12 sub-symbols for 12 subcarriers of each ofthree OFDM signals are shown in FIG. 12, although in a communicationsystem such as the communication system 100 of FIG. 1 employing 48subcarriers, an additional 36 subcarriers may be used. The sub-symbolsfor the additional subcarriers have been omitted from FIG. 12 forreasons of clarity.

The use of a representative embodiment of the present invention as shownin FIG. 12 results a separation of three subcarriers (i.e., tones)between bits in the sequence of output bits 1210, for bits that areadjacent in the block of input bits (not shown).

FIG. 13 illustrates another exemplary sequence of output bits 1310comprising three subsequences of output bits 1320 a, 1320 b, 1320 c fortransmission via, for example, three OFDM transmit signals, where thesequence of output bits 1310 are produced by an interleaver block suchas, for example, the interleaver block 815 of FIG. 8, in accordance witha representative embodiment of the present invention. In therepresentative embodiment illustrated in FIG. 13, bits from a block ofinput bits (not shown) are allocated to sub-symbols in one of threesubsequences 1320 a, 1320 b, 1320 c that may correspond to, for example,one of three transmit streams similar to the transmit streams 318 a, 318b shown in FIG. 3. The illustration of FIG. 13 shows only a portion of ablock of 288 input bits (288=B*K*N, where B=2, K=48, N=3) followingprocessing by an interleaver block such as, for example, the interleaverblock 1015 of FIG. 10. Although the illustration of FIG. 10 shows aninterleaver block 1015 that produces a sequence of output bits 1020comprising two subsequences 1022 a, 1022 b for transmission via two OFDMsignals, the present invention is not limited to the particularembodiment of FIG. 10, and may be applied to produce a greater number oftransmit streams comprising subsequences of output bits. The sequence ofoutput bits 1310 is similar to the sequence of output bits 1110 of FIG.11, with the additional operation of swapping or rotating sub-symbolsbetween the subsequences 1320 a, 1320 b, 1320 c in a manner differentfrom that illustrated in FIG. 12.

In the illustration of FIG. 13, it can be seen that sub-symbols incolumns 1354, 1358, 1362, 1366, 1370, and 1374 have been rotated betweenthe subsequences 1320 a, 1320 b, 1320 c compared to the arrangement ofsub-symbols shown in columns 1154, 1158, 1162, 1166, 1170, and 1174 ofFIG. 11, respectively. In the illustration of FIG. 13, the sub-symbolsassigned to every other subcarrier have been rotate across thesubsequences 1320 a, 1320 b, 1320 c and, therefore, across the OFDMtransmit streams that carry them. For example, in FIG. 11 the bits b₉₆,b₁₁₂ from the block of input bits have been allocated to a sub-symbolfor the second subcarrier (column 1154) of the subsequence 1120 a,whereas in the illustration of FIG. 13, the same bits b₉₆, b₁₁₂ from theblock of input bits are allocated to a sub-symbol for the secondsubcarrier (column 1354) of the subsequence 1320 b. In a similarfashion, in FIG. 11 the bits b₁₂₈, b₁₄₄ that are allocated to thesub-symbol for the second subcarrier (column 1154) of subsequence 1120 bare allocated in the example of FIG. 13 to the second subcarrier (column1354) of subsequence 1320 c. To complete the example, the bits b₁₆₀,b₁₇₆ that are allocated to the second subcarrier (column 1154) ofsubsequence 1120 c in FIG. 11 are instead allocated in the illustrationof FIG. 13 to the second subcarrier (column 1354) of subsequence 1320 a.Similar rotations of sub-symbols between the subsequences 1320 a, 1320b, 1320 c are performed in columns 1362, and 1370 of FIG. 13. Asillustrated in FIG. 13, an interleaver block in accordance with arepresentative embodiment of the present invention may also perform arotation of sub-symbols in columns 1358, 1366, and 1374, where thesub-symbols are rotated from subsequence 1120 a to subsequence 1320 c,from subsequence 1120 b to subsequence 1320 a, and from subsequence 1120c to subsequence 1320 b. Although only 12 sub-symbols for 12 subcarriersof each of three OFDM signals are shown in FIG. 13, in a communicationsystem such as the communication system 100 of FIG. 1 employing 48subcarriers (i.e., tones), an additional 36 subcarriers may be used. Thesub-symbols for the additional subcarriers have been omitted from FIG.13 for reasons of clarity.

The use of a representative embodiment of the present invention asillustrated in FIG. 13 results in a separation of three subcarriers(i.e., tones) between bits in the sequence of output bits 1310, for bitsthat are adjacent in the block of input bits (not shown). However,additional de-correlation of errors in transmitted bits is provided bythe allocation of adjacent bits in the block of input bits to differentsubsequences 1320 a, 1320 b, 1320 c in the sequence of output bits 1310.

The illustration of FIG. 12 uses the mapping (3) discussed above withrespect to FIG. 4, with rot=K, and applies it to the subsequences shownin FIG. 11, which are input into the “bit-to-stream allocator”. It maybe seen from the illustration of FIG. 12 that adjacent bit separation isnot improved. A representative embodiment of the present invention mayemploy a mapping such as the mapping (4) discussed above, in a systemusing three transmit streams. The results of employing such a mappingare illustrated in FIG. 13. From the illustration of FIG. 3 it is clearthat a representative embodiment of the present invention hasaccomplished the desired separation in the subsequences 1320 a, 1320 b,1320 c of adjacent bits of the input symbol.

FIG. 14 is a graph comparing the estimated performance of communicationsystems employing existing (i.e., legacy, IEEE 802.11a/g) interleavingtechniques and one transmit and one receive antenna (1410), no bitinterleaving using one transmit and one receive antenna (1420), a systememploying four transmit and four receive antennas without interleaving(1440), and a system employing four transmit and four receive antennaswith (1430) interleaving in accordance with a representative embodimentof the present invention. The results shown in FIG. 14 for systemsemploying multiple input multiple output (MIMO) configurations (i.e.,curves 1430, 1440) represent the performance of a uniform linear arrayof antennas, spaced at half-wavelength intervals, assuming a 20 MHzsignal bandwidth compliant with the IEEE 802.11n channel model Dtransmitted over a distance of 15 meters, and 64-point quadratureamplitude modulation (QAM) using a code with rate R=½. The receiver wasassumed to employ soft Viterbi decoding, and to exchange packets of 1000bytes in length.

The illustration of FIG. 14 shows that a single receive/single transmitantenna communication system transmitting over a 50 nanosecond delayspread channel using legacy interleaving (curve 1410) is estimated torequire a signal to noise ratio (SNR) of 20 dB to achieve a packet errorrate of 0.1 (10%). In comparison, a similar communication system withoutinterleaving (curve 1420) is estimated to require over 25 dB to achievethe same packet error rate. The performance of a communication systememploying four transmit and four receive antennas (curve 1430) andinterleaving in accordance with a representative embodiment of thepresent invention is expected to achieve a packet error rate of 0.1(10%) at a SNR of 28 dB, however such a system has a higher effectivebit rate due to the simultaneous use of multiple transmit streams. Incontrast, a similar communication system employing four transmit andfour receive antennas without the interleaving of the present invention(curve 1440) is expected to achieve a packet error rate of 0.1 (10%)only at a SNR of more than 36 dB. Such results indicate that employmentof a representative embodiment of the present invention in wireless OFDMcommunication systems similar to IEEE 802.11a/g may be expected toprovide a significant improvement in packet error rate.

As systems are evolving towards multiple antennas, another dimension canbe exploited: space. A representative embodiment in accordance with thepresent invention keeps the interleaver delay to within 1 symbol (as inlegacy devices) but is able to use the spatial dimension to gain moreerror protection.

Aspects of the present invention may be found in an interleaver circuitfor processing bits of an input symbol to form N transmit streams eachcomprising K subsymbols per input symbol. In a representative embodimentof the present invention, each subsymbol may comprise B bits of theinput symbol, and each subsymbol may be communicated via an associatedsubcarrier of an orthogonal frequency division multiplex (OFDM) signal.A representative embodiment in accordance with the present invention maycomprise at least one interleaver performing at least one permutationupon bits of the input symbol. The at least one interleaver may functionto gain tone separation between adjacent bits of the input symbol byspreading bits of the input symbol across the N transmit streams. The atleast one interleaver may comprise a plurality of interleavers. Arepresentative embodiment of the present invention may also comprise abit to stream allocator.

In a representative embodiment of the present invention, bit k of theinput symbol may be mapped to bit i of a first bit sequence according tothe formula:

$i = {{\frac{B\; K\; N}{r}( {k\; {mod}\; r} )} + \lfloor \frac{k}{r} \rfloor}$k = 0, 1, …  , B K N − 1

wherein r denotes interleaving depth; and wherein

$\lfloor \frac{k}{r} \rfloor$

denotes the largest integer not exceeding the value

$\frac{k}{r}.$

In a representative embodiment of the present invention, bit i of thefirst bit sequence may be mapped to bit j of a second bit sequenceaccording to the formula:

$j = {{s\lfloor \frac{i}{s} \rfloor} + {{mod}( {{i + {B\; K\; N} - \lfloor \frac{ri}{B\; K\; N} \rfloor},s} )}}$i = 0, 1, …  , B K N − 1

wherein s=max(B/2,1), and wherein r denotes interleaving depth.

A representative embodiment of the present invention may also comprise ablock mapper that groups B bits of the second bit sequence to formsubsymbols and groups subsymbols into blocks comprising

$\frac{K}{rot}$

subsymbols, and wherein rot is any integer divisor of K. The blocks ofsubsymbols may be distributed across the transmit streams according toan index, m, defined by the formula:

m=(rot*q*(N−1)+p)mod(N*rot)

where p=N*(0: rot−1)+q, and where rot denotes any integer divisor of K,q denotes integer values such that 0≦q≦N−1, N denotes the number oftransmit streams having indexes 0 through N−1, and (0:rot−1) denotes thesequence 0, 1, 2, . . . , (rot−1).

In a representative embodiment of the present invention, the interleavercircuit may be operable in a mode compliant with the Institute ofElectrical and Electronics Engineers (IEEE) 802.11a standard (1999), andthe interleaver circuit may be operable in a mode compliant with theInstitute of Electrical and Electronics Engineers (IEEE) 802.11gstandard (2003).

Further aspects of the present invention may be seen in an interleavercircuit for processing bits of an input symbol for transmission via aplurality of orthogonal frequency division multiplex (OFDM) transmitsignals. Such a circuit may comprise a plurality of interleavers forinterchanging bits of the input symbol, where each of the interleaversmay operate according to an associated permutation. The plurality ofinterleavers may allocate bits of the input symbol to form subsymbols,and each subsymbol may be associated with a subcarrier of one of theplurality of orthogonal frequency division multiplex (OFDM) transmitsignals. The plurality of interleavers may comprise a block mapper forgrouping subsymbols into blocks of subsymbols, and the plurality ofinterleavers may allocate blocks of subsymbols across the plurality oforthogonal frequency division multiplex (OFDM) transmit signals.

Still other aspects of the present invention may be observed in a methodof interleaving bits of an input symbol for transmission over aplurality of transmit antennas. In a representative embodiment inaccordance with the present invention, each of the transmit antennas mayradiate a corresponding one of a plurality of orthogonal frequencydivision multiplex streams, each comprising a plurality of subcarriers.Such a method may comprise interleaving bits of the input symbolaccording to at least one permutation, and allocating interleaved bitsto sub-symbols. The method may also comprise mapping sub-symbols toblocks, and spreading the blocks across the plurality of transmitantennas using the plurality of orthogonal frequency division multiplexstreams, thereby gaining tone separation between adjacent bits of theinput symbol. The at least one permutation may be compliant with theInstitute of Electrical and Electronics Engineers (IEEE) 802.11astandard (1999), the at least one permutation may be compliant with theInstitute of Electrical and Electronics Engineers (IEEE) 802.11gstandard (2003). The interleaved bits may be allocated to subsymbols ofall subcarriers of one of the plurality of orthogonal frequency divisionmultiplex streams, before being allocated to subsymbols of allsubcarriers of another of the plurality of orthogonal frequency divisionmultiplex streams. In a representative embodiment of the presentinvention, an order of allocation of interleaved bits to bits ofsubsymbols may alternate for successive subsymbols.

In a representative embodiment of the present invention, the bits of aninput symbol may be allocated to all subsymbols for one subcarrier ofall of the plurality of orthogonal frequency division multiplex streams,before bits of the input symbol are allocated to all subsymbols ofanother subcarrier of all of the plurality of orthogonal frequencydivision multiplex streams. An order of allocation of interleaved bitsto bits of subsymbols may alternate as subsymbols are allocated to eachof the plurality of orthogonal frequency division multiplex streams.

Additional aspects of the present invention may be seen in amachine-readable storage, having stored thereon a computer programhaving a plurality of code sections executable by a machine for causingthe machine to perform the operations described above.

Accordingly, the present invention may be realized in hardware,software, or a combination of hardware and software. The presentinvention may be realized in a centralized fashion in at least onecomputer system, or in a distributed fashion where different elementsare spread across several interconnected computer systems. Any kind ofcomputer system or other apparatus adapted for carrying out the methodsdescribed herein is suited. A typical combination of hardware andsoftware may be a general-purpose computer system with a computerprogram that, when being loaded and executed, controls the computersystem such that it carries out the methods described herein.

The present invention may also be embedded in a computer programproduct, which comprises all the features enabling the implementation ofthe methods described herein, and which when loaded in a computer systemis able to carry out these methods. Computer program in the presentcontext means any expression, in any language, code or notation, of aset of instructions intended to cause a system having an informationprocessing capability to perform a particular function either directlyor after either or both of the following: a) conversion to anotherlanguage, code or notation; b) reproduction in a different materialform.

While the present invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiment disclosed, but that the present invention willinclude all embodiments falling within the scope of the appended claims.

What is claimed is:
 1. A wireless device comprising: a wirelessinterface; and processing circuitry, the wireless interface andprocessing circuitry operable to: interleave bits of an input symbol toform N orthogonal frequency division multiplex (OFDM) transmit streamsacross K subcarriers, wherein at least one input symbol comprises KNsubsymbols, wherein at least one of the KN subsymbols comprises B bitsof the input symbol, and wherein at least one subsymbol is communicatedvia an associated subcarrier of the N transmit streams, the interleavingincluding: permutating at least some bits of the input symbol; block mapgrouping permutated bits into subsymbols; grouping the subsymbols intoblocks of subsymbols; spreading the bits across the N transmit streamsbefore the bits are spread across the K subcarriers; and rotating thesubsymbol blocks between the N transmit streams, wherein N is greaterthan 1.